A reaction between benzene and propylene gives cumene. Oxidation of cumene results in cumene hydroperoxide. The cumene hydroperoxide is acid decomposed into phenol and acetone. A combination of these known reactions is the cumene process which is currently a mainstream process for the production of phenol.
The cumene process gives acetone as a by-product, and is valuable when both phenol and acetone are required. However, if the acetone produced is in excess of demand, the economic efficiency is deteriorated due to the price difference between acetone and starting material propylene. Methods have been then proposed which are aimed at benefiting from the price difference between starting material olefins and by-product ketones. For example, secondary butyl benzene obtained from n-butene and benzene is oxidized and acid decomposed to give phenol and methyl ethyl ketone (Patent Documents 1 and 2). According to this method, the oxidation of the secondary butyl benzene achieves only about 80% selectivity for the target secondary butyl benzene hydroperoxide, with 15% or more by-product acetophenone. This method consequently provides a lower yield of phenol than by the cumene process.
It is also proposed that cyclohexyl benzene obtained from cyclohexene and benzene is oxidized and acid decomposed into phenol and cyclohexanone. Since the cyclohexanone obtained is dehydrogenated into phenol, this method does not technically involve the by-production of ketones. However, the method has a low industrial value because the oxidation of the cyclohexyl benzene provides a low yield of the target cyclohexyl benzene hydroperoxide.
The highest yields in oxidation and acid decomposition are achieved by the cumene process as described above. The problem related to starting material propylene and by-product acetone should be avoided while maintaining the advantageous yields. Methods have been then proposed in which the by-product acetone is treated by various methods and is reused as a material in the cumene process.
Acetone is readily hydrogenated to isopropanol, and the isopropanol is dehydrated to propylene. Patent Document 3 discloses a process in which acetone is reused as a material in the cumene process, in detail cumene is produced by reacting benzene and propylene obtained from acetone as described above. However, the hydrogenation and the dehydration add two steps.
Patent Documents 4 to 6 disclose methods in which isopropanol from the hydrogenation of acetone is directly reacted with benzene to give cumene. In particular, Patent Document 6 discloses a process in which by-product acetone is hydrogenated to isopropanol, the isopropanol is reacted with benzene, and the resultant cumene is reacted to give phenol. In this process, however, the hydrogenation adds a step to the cumene process.
Patent Document 7 describes a method in which by-product acetone is reused without adding a step to the conventional cumene process. In detail, acetone is reacted directly with benzene in the presence of hydrogen using a catalyst system including a solid acid substance and a Cu compound.